Catching the Lightwave

"Our development reinforces the practicality of the new field of nanooptomechanics," says Hong Tang, assistant professor of electrical and mechanical engineering in the Yale School of Engineering and Applied Sciences. "Furthermore, it points to a future of compact, robust and scalable systems with high sensitivity that will find a wide range of future applications - from chemical and biological sensing to optical signal processing."

In nanoelectromechanical systems (NEMS), cantilevers are the most fundamental mechanical sensors. These tiny structures - fixed at one end and free at the other - act like nano-scale diving boards that "bend" when molecules "jump" on them and register a change that can be measured and calibrated. The study shows how NEMS can be improved by using integrated photonics to sense the cantilever motion.

"The system we developed is the most sensitive available that works at room temperature. Previously this level of sensitivity could only be achieved at extreme low temperatures", said Tang.

Their system can detect as little deflection in the nano-cantilever sensors as 0.0001 Angstroms - one ten thousandth of the size of an atom

To detect this tiny motion, the Yale team devised a photonic structure to guide the light wave through a cantilever. After exiting from the free end of the cantilever, the light tunnels through a nanometre gap and is collected on chip. "Detecting the lightwave after this evanescent tunneling," says Tang, "gives the unprecedented sensitivity."

Tang's group "wired" the sensors with light in a novel way. Their technique is not limited by the bandwidth constraints of electrical methods or the diffraction limits of light sources.

"We don't need a laser to operate these devices," said Wolfram Pernice. "Very cheap LEDs will suffice." Futhermore, the LED light sources - like the million LED pixels that make up a laptop computer screen - can be scaled in size to integrate into a nanophotonic-chip - an important feature for this application.